JOHNS HOPKINS (US) — Donated blood stored longer than three weeks begins to lose capacity to deliver oxygen-rich red blood cells where they may be most needed, a study indicates.

In a new report adding to evidence on the issue, investigators say red cells in blood stored for that long gradually lose the flexibility they need to squeeze through the body’s smallest capillaries to deliver oxygen to tissue. That flexibility is not regained after transfusion into patients during or after surgery, they say.

“There’s more and more information telling us that the shelf life of blood may not be six weeks, which is what the blood banks consider standard,” says Steven M. Frank, associate professor of anesthesiology and critical care medicine at the Johns Hopkins University School of Medicine. “If I were having surgery tomorrow, I’d want the freshest blood they could find.”

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Blood banks do not have enough fresh blood for everybody, and shorter storage periods would result in diminished inventory, acknowledges Frank, the leader of the study. But the current practice of transfusing blood stored up to six weeks may need to be reconsidered, he says.

A previous study showed that cardiac surgery patients who received blood stored longer than three weeks were almost twice as likely to die as patients who got blood that had been stored for just 10 days.

For the new study, published online in the journal Anesthesia & Analgesia,Frank and colleagues enrolled 16 patients scheduled to have spinal fusion surgery, which typically requires blood transfusions. Six received five or more units of blood, while 10 needed three or fewer.

The researchers drew samples from every bag of blood used—53 in total—and measured the flexibility of the red blood cells. They found that blood older than 3 weeks was more likely to have less flexible red blood cell membranes, a condition that may make it more difficult for blood to deliver oxygen.

The team also took blood samples from patients in the three days following surgery. Even though the blood cells were out of storage and back in biological environments with proper acidity, electrolyte, and oxygen levels, the injury to the red cells did not reverse and appeared to be permanent. The damaged blood cells would likely remain dysfunctional for their life cycle limit, which is up to 120 days, Frank says.

Patients in the study who got fewer units of blood had healthier red cells overall, even though the transfused blood was just as old and showed cell damage. A small number of these problem cells may make less of a difference than when a large number of damaged cells are present, Frank says.

The average shelf age of the blood given in the study was more than 3 weeks. Only three samples in the study were 2 weeks old or less. One reason for the lack of availability of fresher bloods for adults, Frank says, is the routine practice of giving pediatric patients priority for the freshest units.

In fact, he notes, blood banks dispense the oldest blood first so that it doesn’t exceed its shelf life before it can be used.

“As a colleague said, it’s like how they sell milk in the grocery store; they put the oldest cartons out front so they can sell them before they expire,” Frank says.

Two large randomized controlled studies, one at many centers across the United States, including Johns Hopkins, and one in Canada, are under way to determine the relative safety of older versus newer blood, and the results are expected next year. Blood banks need to be prepared to change practice if those studies show that a six-week shelf life for blood is just too long.

The study was supported in part by the National Institutes of Health’s National Institute on Aging and National Heart, Lung, and Blood Institute.

One of the researchers who worked on the study has consulted for Terumo BCT and Fenwal Labs, both companies involved with blood storage. Nothing in the study directly benefits those companies. The terms of these arrangements are being managed by the Johns Hopkins University in accordance with its conflict of interest policies.